8160

• UCREFRP Catalog Number: 8160
• Author: Trammell, M. and T. Chart.
• Title: Aspinall Studies
• USFW Year: 1999.
• USFW - Doc Type: Evaluation of Nursery Habitat Availability and Colorado Pikeminnow Young of Year Habitat Use, in the Colorado River, Utah, 1992-1996\
• Copyright Material: NO

Hydrograph, sampling flows, and physical habitat
Flows in the Colorado River at the Cisco, UT gage (LTSGS gage #09180500) are ~
influenced, but not controlled, by flows from the Gunnison River. The Gunnison joins the
Colorado River near Grand Junction, Colorado, where it usually contributes about half the flow
seen at the confluence during base flows, and less during peak flows. Several smaller tributaries
also contribute flows between the Gunnison and the Cisco gage, including the Dolores River,
which contributes an average of 3000 cfs to the peak flows. All analyses using flows were based ~
on the Cisco gage, to account for the contributions of the tributaries.
The average spring peak runoff flow was 36,155 cfs for the period of record (1914-1996)
which encompasses both pre- and post-regulation periods for the Colorado River, near Cisco.
The historic peak (pre-regulation) was 73,200 cfs, and the highest post-regulation peak (after
1961) was 69,500 cfs which occurred in 19$4. Interestingly, the 3ra and 4"' highest peaks for the ~
period of record occurred during this study in 1995 and 1993. Based on the average peak, this
study encompassed 21ow water years, 1992 and 1994 (<50% of avg.), 2 high water years 1993
and 1995, (>130% of avg.) and one moderate year, 1996 (80% of avg.) (Figure 2). Physical
habitat variables were summarized for each sampling occasion. The data are grouped by year
and season in Tables 5 and 6. ~
Sampling flows ranged from 2250 in summer 1994, to 8380 cfs in summer 1995 (flow
had increased prior to trip due to rainfall). Most of the sampling flows above 5000 cfs were
encountered during the spring sampling. Total habitat area was highly variable, ranging from
3073 mZ in the fall of 1995, to 28299 m2 in the fall of 1992, in the lower section, and 8856 mZ in
the fall of 1994, to 23957 mZ in the summer of 1992 in the upper section. There was a greater ~
amount of habitat available in the upper section on most sampling occasions. The number of
habitats varied from 13 to 43, with the fewest sites seen in the spring. Within each year, the
average depth of all habitats was usually greatest in the summer period.

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